My fingers turn grey when cold. .. is this bad?

Raynauds: This sounds to me like Raynauds It may occur in 5 % of the population. The underlying cause is often unknown but there are some diseases that have this as a symptom. http://www.nhlbi.nih.gov/health/health-topics/topics/raynaud/

Raynaud's?: There is a fairly common condition called Raynaud's syndrome, in which blood vessels constrict abnormally when cold. It's usually just a comfort issue, but rarely cases it is an early sign of a more serious problem, or can be so bad it results in dangerously reduced blood supply to the fingertips. Google it for more info and photos. Tell your parents, and see your doctor for professional advice.